Flowable material retainers, including containers or conduits, formed from flexible sheet materials have found or are adaptable to a broad range of applications. For example, such retainers may be employed as plasma bags, colostomy bags, fluid conduits, or packages for storing flowable materials, e.g., fluids, powders, or semi-fluid materials. Retainers formed from flexible materials have proved popular in part because they are relatively simple and inexpensive to produce, particularly if formed from sheet materials which can be heat sealed together to form a retainer body, and are deformable to facilitate storage or deployment of the retainer in compact or irregularly shaped areas.
In many applications, it is important that a closure device be provided which is capable of sealably closing the flexible retainer. For example, in the case of plasma bags, a reliable closure must be formed to prevent escape or contamination of the plasma. One method of closing a flexible retainer is by exerting a clamping force on opposing walls of the retainer thereby pressing the walls together to form a closure to inhibit flow of material therebetween. A difficulty encountered in connection with such closure devices is the tendency for the closure to fail when an expansion force is exerted thereon. Such expansion forces are exerted, for example, when the flowable material flows towards the closure urging the opposing walls apart in the vicinity of the closure. Flow towards the closure may result when a compression force is exerted on the retainer, such as when weight is placed on the retainer or the retainer is squeezed, or when the retainer is turned so that material flows towards the closure due to gravitational forces. It is desirable that a closure device be provided wherein the clamping force pressing the opposing walls together increases to counteract expansion forces resulting when material flows towards the closure.
One device for closing a flexible retainer is disclosed in U.S. Pat. No. 3,217,934. Two flexible sheets are sealed together to form walls of a package body and a discharge channel which tapers from the package body to an open end. One of the package walls has a slit therein and a means, such as a flexible strip, is applied to the inner face of the wall to prevent the contents of the package from escaping through the slit. The package is closed by folding the package along a line transverse to the discharge channel and inserting the open end into the slit. Presumably, the container walls are pressed together to form a closure thereby inhibiting passage of the container contents therethrough when the package is closed. However, the patent does not disclose a device whereby the force pressing the walls together increases to counteract increasing expansion forces resulting when material flows towards the closure. In addition, the patent does not disclose a closure device for retaining gases.
Other devices for closing flexible retainers provide a separate piece, such as a lid or clamp, which can be attached to the retainer body thereby closing the retainer. However, such devices have the disadvantage that the separate piece may be lost resulting in inconvenience to the user. In addition, the need for a separate piece increases the expense and difficulty of manufacture.
Also known are closure devices wherein mating elements are provided on opposing walls of the package so that the package may be closed by interlocking the elements, for example, zip-lock bags. However, the provision of such elements increases the difficulty and expense of production. Moreover, such closure devices do not provide a method whereby the forces pressing the opposing walls together increase to counteract expansion forces resulting when material flows towards the closure. In fact, such closure devices are typically reopened in ordinary use by pulling the opposing walls apart to break the closure.
Thus, there is a need for a closure device for closing flexible retainers wherein a clamping force increases to counteract expansion forces exerted on the closure due to material flow towards the closure. Preferably, such a device would be simple and inexpensive to produce yet capable of sealably retaining a broad range of flowable materials.